Arc-fault interruption (AFI) and ground-fault interruption (GFI) circuit breakers are well known. Such circuit breakers have traditionally required an extra conductor, called a “pigtail,” to connect the breaker to a line-side neutral conductor of an electrical distribution panel or load center (these terms are used interchangeably herein). Increased use of arc-fault circuit breakers in a residential load center results in additional pigtails crowding the wiring gutter of the load center, making it more difficult to wire as more circuit breakers are added and creating a jumble of wires. Furthermore, to wire the pigtail, the installer must connect the wire at the side line neutral conductor using a tool, thereby making the wiring more time consuming.
More recently, AFI and GFI circuit breakers feature a “plug-on neutral” (PON or PoN), which replaces the pigtail, and allows the circuit breaker to be “plugged onto” the neutral bus bar directly. Instead of a pigtail, the circuit breaker has a connector called a neutral clip that directly plugs onto the neutral conductor in the electrical distribution panel. The neutral clip typically faces downward away from a bottom surface of the circuit breaker so that it is oriented to be plugged directly onto a neutral conductor in the electrical panel or load center. However, certain disadvantages remain when accommodating plug-on-neutral circuit breakers as well as pigtail-neutral circuit breakers in the same panel because both circuit breaker types are widely used. For example, one known type of hybrid neutral bus bar utilizes a square screw down rail, which has a flat and even top surface through which to insert a tightening screw (also known as a “hold down screw”) for use with a wire type circuit breaker or on which to secure a neutral clip of a PON circuit breaker. The flat top surface of the rail makes it difficult to properly secure a neutral clip of a PON circuit breaker onto the rail. Furthermore, the tightening screws, which extend above the top surface of the rail when engaged therein, also may interfere with proper connection of the neutral clip onto the rail.